The present invention relates generally to a method for high accuracy placement of a first workpiece onto a second workpiece for attachment of the two workpieces, and more particularly to a high accuracy placement method which utilizes double pick and place of the first workpiece to enhance the final placement accuracy of the first workpiece onto the second workpiece.
Many applications in the electronics industry require attachment of electronic components to one another. Die attach is an attachment method which has particular utility to the microelectronics industry. The basic principles of soldering apply to die attach, but die attach is specific to attachment of a die to a circuit body. The die is typically a tiny semiconductor device such as a diode or transistor and the circuit body is typically a larger structure such as a substrate or a package on which the die is mounted. Attachment of the die to the circuit body is preceded by a pick and place operation, wherein the die is picked from a remote location by a tool and placed on the circuit body at the location where attachment is desired. Thereafter, the die and circuit body are heated to the melting point of an interposed solder, more specifically termed the die attach material, to form an electrically and thermally conductive die attach connection between the die and the circuit body.
It is generally desirable to automate die attach, including the pick and place operation, to achieve the high output rates required for most industrial applications. For example, the optical communications industry requires large volumes of laser diodes attached to packages or substrates by die attach. Nevertheless, such applications also have very narrow placement tolerances with respect to placement of the die on the package or substrate for satisfactory performance of the resulting product, e.g., on the order of 1 to 5 microns. Conventional machines are not able to perform pick and place operations in a sufficiently accurate manner to achieve the required placement tolerances of most optical communications applications. As such, the present invention both recognizes and solves the need for an automated placement method, which is sufficiently accurate for the most demanding microelectronic applications.
Accordingly, it is an object of the present invention to provide an automated placement method which is both time efficient and highly accurate. More particularly, it is an object of the present invention to provide an automated placement method which processes a workpiece pair by placing the first workpiece onto the second workpiece with a high degree of accuracy and precision and thereafter attaching the first workpiece to the second workpiece. These objects and others are accomplished in accordance with the invention described hereafter.
The present invention is a method for placement of a first workpiece onto a second workpiece. The first workpiece is initially positioned at an origination location and the second workpiece has an attach location different from the origination location. A first place step is performed to displace the first workpiece from the origination location to an intermediate location different from the origination and attach locations. A second place step is performed to displace the first workpiece from the intermediate location to the attach location and the first workpiece is attached to the second workpiece at the attach location.
In accordance with a more specific embodiment, the present invention is a method for placement of a first workpiece, which is preferably a die, onto a second workpiece, which is preferably a circuit body. The first workpiece is initially positioned at an origination location which is different from a target intermediate location. The second workpiece is positioned at a work location and has a target attach location which is different from the target intermediate location and the origination location. A first place step is performed to displace the first workpiece from the origination location to an actual intermediate location. Displacement of the first workpiece from the origination location to the actual intermediate location is preferably performed with reference to a first place path determined by referencing the target intermediate location. A first pick step is preferably performed in advance of the first place step by engaging the first workpiece with a pickup tool at the origination location. Displacement of the first workpiece in the first place step is effected by displacing the pickup tool while engaging the first workpiece. The pickup tool is then preferably disengaged from the first workpiece at the actual intermediate location. The actual intermediate location is different from the origination location and is identical to the target intermediate location or differs from the target intermediate location by an intermediate error deviation. The intermediate error deviation is preferably between about 0 and 5 degrees with respect to a rotational reference axis or between about 0 and 15 microns with respect to linear reference axes.
A second place step is performed to displace the first workpiece from the actual intermediate location to an actual attach location on the second workpiece. Displacement of the first workpiece from the actual intermediate location to the actual attach location is preferably performed with reference to a second place path determined by referencing the target attach location. A second pick step is preferably performed in advance of the second place step by reengaging the first workpiece with the pickup tool at the actual intermediate location and displacing the first workpiece in the second place step by displacement of the pickup tool while engaging the first workpiece. The actual attach location is different from the origination location and the target intermediate location and is identical to the target attach location or differs from the target attach location by an attach error deviation. The attach error deviation is preferably between about 0 and 2 degrees with respect to a rotational reference axis or between about 0 and 10 microns with respect to linear reference axes and the attach error deviation is more preferably less than the intermediate error deviation.
The first workpiece is then attached to the actual attach location. In accordance with one alternative, the first workpiece is thermally attached to the actual attach location by heating the first or second workpiece or both first and second workpieces to a thermal attachment temperature sufficient to effect thermal attachment of the first workpiece to the actual attach location. The first workpiece may be preheated before the second place step to a background temperature less than the thermal attachment temperature. Soldering is a preferred thermal attachment means.
The method of the present invention is preferably performed repetitively in successive cycles on succeeding first and second workpiece pairs. As such, the first cycle has been described above, wherein the first workpiece is a first pair first workpiece of the first workpiece pair and the second workpiece is a first pair second workpiece of the first workpiece pair. The origination location is a first pair origination location and the target attach location is a first pair target attach location. A second cycle is initiated by displacing the first pair second workpiece from the work location. The second workpiece pair consists of a second pair first workpiece and a second pair second workpiece. The second pair first workpiece is positioned at a second pair origination location different from the target intermediate location and the first pair origination location. The first and second pair origination locations are preferably on a carrier. The second pair second workpiece has a second pair target attach location and is positioned at the work location such that the second pair target attach location corresponds identically to the first pair target attach location when the first pair second workpiece was positioned at the work location.
A second pair first place step is performed to displace the second pair first workpiece from the second pair origination location to a second pair actual intermediate location. The second pair actual intermediate location is different from the second pair origination location and is identical to the target intermediate location or differs from the target intermediate location by a second pair intermediate error deviation. A second pair second place step is performed to displace the second pair first workpiece from the second pair actual intermediate location to a second pair actual attach location on the second pair second workpiece. The second pair actual attach location is different from the second pair origination location and the target intermediate location and is identical to the second pair target attach location or differs from the second pair target attach location by a second pair attach error deviation. The second pair first workpiece is attached to the second pair actual attach location following the second pair second place step.
Another method of performing the present invention repetitively in successive cycles on succeeding first and second workpiece pairs is provided in the alternative. The first cycle remains as described above. However, the second cycle differs from the second cycle described above insofar as the second workpiece of the first workpiece pair is also the second workpiece of the second workpiece pair. The second workpiece pair further consists of a second pair first workpiece, which is distinct from the first pair first workpiece. The second pair first workpiece is positioned at a second pair origination location different from the target intermediate location and the first pair origination location. The second workpiece has a second pair target attach location different from the first pair target attach location. A second pair first place step is performed to displace the second pair first workpiece from the second pair origination location to a second pair actual intermediate location. The second pair actual intermediate location is different from the second pair origination location and is identical to the target intermediate location or differs from the target intermediate location by a second pair intermediate error deviation.
A second pair second place step is performed to displace the second pair first workpiece from the second pair actual intermediate location to a second pair actual attach location on the second workpiece. The second pair actual attach location is different from the second pair origination location, the target intermediate location, and the first pair target and actual attach locations and is identical to the second pair target attach location or differs from the second pair target attach location by a second pair attach error deviation. The second pair first workpiece is attached to the second pair actual attach location following the second pair second place step.
Another method of performing a single cycle of the present invention is further provided in the alternative. The present embodiment of the first cycle differs from the embodiment of the first cycle described above only insofar as the target intermediate location is identical to the target attach location of the second workpiece. Yet another alternative for performing the present invention repetitively in successive cycles on succeeding first and second workpiece pairs is provided wherein the second pair second workpiece is distinct from the second pair second workpiece. This alternative differs from those recited above only insofar as the target intermediate location is identical to both the first pair and second pair target attach locations of the first pair and second pair second workpieces, respectively. Still another alternative for performing the present invention repetitively in successive cycles on succeeding first and second workpiece pairs is provided wherein the second workpiece of the first and second workpiece pairs are the same workpiece. This alternative differs from those recited above insofar as the target intermediate location is a first pair target intermediate location, which is identical to the first pair target attach location of the second workpiece. The second workpiece also has a second pair target attach location which is identical to a second pair target intermediate location.
The present invention will be further understood from the drawings and the following detailed description.